Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$88.90	12.686%	$100.1779	$100.18	$100.20	$100.20
Purchase #2	$64.29	9.607%	$70.4663	$70.47	$70.45	$70.50
Purchase #3	$129.76	11.136%	$144.2101	$144.21	$144.20	$144.20
Purchase #4	$194.35	11.473%	$216.6478	$216.65	$216.65	$216.60
Purchase #5	$149.52	5.823%	$158.2265	$158.23	$158.25	$158.20
Purchase #6	$128.75	10.275%	$141.9791	$141.98	$142.00	$142.00
Purchase #7	$146.77	4.757%	$153.7518	$153.75	$153.75	$153.80
7 purchase totals =	$902.34		$985.4595	$985.47	$985.50	$985.50